Modest results from a federal trial of an experimental drug helped send the stock market soaring on Wednesday, another sign of the desperation for a viable treatment against the coronavirus.

Just before markets opened, Gilead, maker of the antiviral drug remdesivir, announced that it was “aware of positive data” about the drug’s performance in a federal trial, sending futures upward. Trading in the company’s shares was briefly halted.

Later, in a briefing at the White House, Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said the trial had shown that treatment with the drug could modestly speed recovery in patients infected with the coronavirus.

The improvement in recovery times “doesn’t seem like a knockout 100 percent,” Dr. Fauci conceded, but “it is a very important proof of concept, because what it has proven is that a drug can block this virus.”

Business leaders, scientists and politicians alike are scrambling to find ways to fight an insidious epidemic and to reopen a devastated economy. The virus has claimed at least 60,000 lives in the United States, and more than 200,000 worldwide. There have been precious few reasons for optimism, and the markets seized on the news.

The trial sponsored by the National Institute of Allergy and Infectious Diseases enrolled 1,063 patients who were given remdesivir or a placebo. The time to recovery averaged 11 days among those who got the drug, compared with 15 days for those who got the placebo.

There were fewer deaths in the remdesivir group, but the result did not reach statistical significance, Dr. Fauci said. Deaths were not a primary measure in the trial.

Dr. Fauci cautioned that the results of the study still needed to be properly peer-reviewed, but he was optimistic that remdesivir would become “the standard of care” for patients with Covid-19.

Some scientists were unsettled by the way in which the findings were reported. The disclosure of trial results in a political setting, before peer review or publication, is very unusual, said Dr. Steven Nissen, a cardiologist at the Cleveland Clinic who has conducted dozens of clinical trials.

“Where are the data?” he asked. Scientists will need to see figures on harms associated with the drug in order to assess its benefits, he added.

“This is too important to be handled in such a sloppy fashion,” Dr. Nissen said.

Dr. Michele Barry, a global health expert at Stanford University, said she had faith in Dr. Fauci’s assessment. Still, she added, “It is unusual to call a drug the ‘standard of care’ until peer review of data and publication, and before studies have shown benefit in mortality.”

The Food and Drug Administration is likely at some point to announce an emergency approval for remdesivir, a senior administration official told The New York Times. Another drug touted by the president, hydrochloroquine, also was granted such an approval, but results in patients have been disappointing.

In one study of veterans with Covid-19, those receiving hydrochloroquine and an antibiotic died at higher rates than those given ordinary supportive care.

Mr. Trump also hopes to put in place a crash program to develop a vaccine, an undertaking being seen with skepticism even inside the administration. The accelerated process, known internally as Operation Warp Speed, would aim to produce hundreds of millions of doses by the end of this year.

But medical experts, including Dr. Fauci, have warned that developing a vaccine will require a year to 18 months at the earliest, and that rushing the process could endanger public health.

For now, drug treatment seems a more attainable goal.

“Remdesivir is not a magic bullet, but it’s as good as we get right now,” said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, and one of the trial’s investigators.

“Patients come to the hospital thinking we have a treatment, and by treatment, they mean a drug,” he added. “We have been impotent in not having any options.”

Remdesivir has never been approved as a treatment for any disease. It was developed to fight Ebola, but results from a clinical trial in Africa were disappointing.

But as the coronavirus pandemic took hold, the drug emerged as one of the more promising potential treatments. It interrupts the production of the virus in lab studies and seems safe in animals.

Until now, high expectations for remdesivir have been fueled largely by anecdotal reports of Covid-19 patients who took the drug and recovered.

Frequently Asked Questions and Advice

Updated June 5, 2020

How many people have lost their jobs due to coronavirus in the U.S.?

The unemployment rate fell to 13.3 percent in May, the Labor Department said on June 5, an unexpected improvement in the nation’s job market as hiring rebounded faster than economists expected. Economists had forecast the unemployment rate to increase to as much as 20 percent, after it hit 14.7 percent in April, which was the highest since the government began keeping official statistics after World War II. But the unemployment rate dipped instead, with employers adding 2.5 million jobs, after more than 20 million jobs were lost in April.

Will protests set off a second viral wave of coronavirus?

Mass protests against police brutality that have brought thousands of people onto the streets in cities across America are raising the specter of new coronavirus outbreaks, prompting political leaders, physicians and public health experts to warn that the crowds could cause a surge in cases. While many political leaders affirmed the right of protesters to express themselves, they urged the demonstrators to wear face masks and maintain social distancing, both to protect themselves and to prevent further community spread of the virus. Some infectious disease experts were reassured by the fact that the protests were held outdoors, saying the open air settings could mitigate the risk of transmission.

How do we start exercising again without hurting ourselves after months of lockdown?

Exercise researchers and physicians have some blunt advice for those of us aiming to return to regular exercise now: Start slowly and then rev up your workouts, also slowly. American adults tended to be about 12 percent less active after the stay-at-home mandates began in March than they were in January. But there are steps you can take to ease your way back into regular exercise safely. First, “start at no more than 50 percent of the exercise you were doing before Covid,” says Dr. Monica Rho, the chief of musculoskeletal medicine at the Shirley Ryan AbilityLab in Chicago. Thread in some preparatory squats, too, she advises. “When you haven’t been exercising, you lose muscle mass.” Expect some muscle twinges after these preliminary, post-lockdown sessions, especially a day or two later. But sudden or increasing pain during exercise is a clarion call to stop and return home.

My state is reopening. Is it safe to go out?

States are reopening bit by bit. This means that more public spaces are available for use and more and more businesses are being allowed to open again. The federal government is largely leaving the decision up to states, and some state leaders are leaving the decision up to local authorities. Even if you aren’t being told to stay at home, it’s still a good idea to limit trips outside and your interaction with other people.

What’s the risk of catching coronavirus from a surface?

Touching contaminated objects and then infecting ourselves with the germs is not typically how the virus spreads. But it can happen. A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals. But a long chain of events has to happen for the disease to spread that way. The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.

How can I protect myself while flying?

If air travel is unavoidable, there are some steps you can take to protect yourself. Most important: Wash your hands often, and stop touching your face. If possible, choose a window seat. A study from Emory University found that during flu season, the safest place to sit on a plane is by a window, as people sitting in window seats had less contact with potentially sick people. Disinfect hard surfaces. When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down, too. (Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.)

Should I wear a mask?

The C.D.C. has recommended that all Americans wear cloth masks if they go out in public. This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms. Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing. Part of the reason was to preserve medical-grade masks for health care workers who desperately need them at a time when they are in continuously short supply. Masks don’t replace hand washing and social distancing.

What should I do if I feel sick?

If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.

“Unfortunately, our trial found that while safe and adequately tolerated, remdesivir did not provide significant benefits over placebo,” said the lead investigator of the new study, Dr. Bin Cao of the China-Japan Friendship Hospital and Capital Medical University in Beijing.

“This is not the outcome we hoped for,” he added.

The results are hard to interpret, because the study was far smaller than planned — enrolling 236 patients instead of the 453 that had been expected, because there were too few severely ill patients now in China.

Dr. Eric Peterson, a clinical trials expert at Duke University, said that with too few patients, “all you can say is it doesn’t seem to work in this population.” If there had been a big effect of the drug, he added, that would have been seen.

He added that the trial should not be repeated with this population, but instead in those who are less severely ill.

“This is a flawed study,” Dr. Barry said, but results might improve if the drug were given at a higher dose or earlier in the course of the disease.

Acceding to demands, Gilead has distributed the drug to hundreds of patients under so-called compassionate use, a regulatory exemption by which patients may receive a drug apart from a clinical trial.

Gilead itself published reports of uncontrolled studies. On Wednesday, in another news release, the company announced that a study comparing a five- to 10-day course of treatment with the drug showed that those getting the shorter course of treatment did just as well.

That study had no control group and was “noninformative,” Dr. Peterson said.